An electric motor often includes a protector capable of shutting down the motor before it is damaged due to an abnormality such as excessive heat. A typical protector is electrically connected to the winding and is adapted to break the current through the winding when the protector senses excessive temperature and/or current in the winding.
Protectors may be “on-winding” protectors, which are mounted directly on the windings, or “off-winding” protectors, which are mounted in a position remote from the windings. It is often beneficial to use on-winding protectors so that the thermal sensor is more responsive to changes in temperature in the windings. By measuring the temperature at the windings, e.g., without a significant gap between the windings and the sensor, the protector can respond more quickly to break current when the windings overheat.
In some cases, however, mounting the protector directly on the windings may make the sensor over-sensitive to changes in temperature in the windings. Moreover, while the properties of the protector may be changed to try to make the sensor less sensitive, applicants have discovered cases where no protector is suitable due to the proximity of the protector to the windings. In some applications, the protector will “open” or “trip” prematurely so that, for example, the motor will fail the Underwriters Laboratory Maximum Carry Current (ULMCC) test. While “off-winding” protectors or sensor/controller arrangements may be used, applicants have found these are not always a satisfactory, cost-effective solution.